For the convenience of use, the touch panel or the display touch panel (having both display and touch functions), which accepts data/instruction from the user or user's click, is widely used in various electronic devices such as mobile phone. Thus, the user can directly input data/instruction or click on the touch panel or the display touch panel and such operation mode is convenient and friendly to the user. There are a variety of touch panels or display touch panels, such as capacitive touch panel or capacitive display touch panel.
When the user operates a capacitive touch panel, a capacitive display touch panel, or a capacitive switch, the capacitance of the capacitor under test thereof varies. Thus, the user's operation will be detected (sensed) if the capacitance of the capacitor under test and its variance can be detected. The capacitive touch panel detects the position of the touch point according to the capacitance variance of the sensing grid embedded in the touch panel.
FIG. 1A shows a conventional touch panel 10. Referring to FIG. 1A. The touch panel 10 includes a plurality of X-direction wires X1˜Xm and a plurality of Y-direction wires Y1˜Yn, m and n are both positive integers being identical or different from each other. The X-direction wires and the Y-direction wires are formed in different layers. The X-direction wires and the Y-direction wires are intersected to form a sensing grid. A cross coupling capacitor, (such as the cross coupling capacitor 100a, 100b or 100c in FIG. 1A) is formed at each of the intersection by the X-direction wire and Y-direction wire. Let FIG. 1A be taken for example, the touch panel 10 has m*n cross coupling capacitors in total.
When an object (such as a finger or a stylus) touches the touch panel 10, the coupling relationship between the object and the sensing grid will change capacitances of nearby cross coupling capacitors. A detection circuit can thus detect the location of the touch point according to the capacitance variance of the cross coupling capacitors.
In operation, a driving signal (such as a squared wave, a triangular wave, a cosine wave, and so on) is inputted to the Y (or X) direction wires. Whether the wires are touched is determined by comparing the coupling voltage on the X (or Y) direction wires. However, an RC delay will occur due to the resistance of the direction wires as well as the internal parasitic capacitance of the touch panel. The internal parasitic capacitance includes the GND parasitic capacitance of the direction wire and the cross-coupling capacitance between the direction wires.
FIG. 1B shows an RC delay according to a prior art. In FIG. 1B, a clock signal clk is a driving signal or an operating clock; and another clock signal clk′ is the driving signal received by the direction wires on the touch panel. IN(−) and IN(+) are respectively a negative input signal and a positive input signal of a sensing circuit (not illustrated). Due to the RC delay, the driving signal received by a far direction wire takes a longer time to stabilize, so the frequency of the driving signal cannot be too high. As the sensing circuit is under control of the driving signal, the sensing rate is affected and slowed down accordingly.